1. Field of the Invention
The present invention relates to a device for controlling the rise of the catalyst temperature in a spark ignition-type internal combustion engine to meet exhaust gas regulations and, particularly, to a device for controlling the rise of the catalyst temperature in an internal combustion engine, which is capable of quickly raising the catalyst temperature up to an activating temperature.
2. Prior Art
The exhaust pipe of an internal combustion engine has heretofore been provided with a catalyst for removing exhaust gas components. The catalyst works at an activating temperature. When the internal combustion engine is cold, therefore, the temperature of the catalyst must be raised by, for example, exhaust gases of a high temperature.
In a conventional device for controlling the rise of the catalyst temperature in an internal combustion engine, therefore, a technology has been proposed such as delaying the ignition timing to promote the rise of the catalyst temperature at the start.
In a device for removing exhaust gas components disclosed in, for example, Japanese Unexamined Utility Model Publication (Kokai) No. 79212/1976, the heated secondary air is introduced into the intake system, and the ignition timing is delayed to quickly raise the temperature of the catalyst at the start.
FIG. 38 is a diagram illustrating the constitution of a conventional device for controlling the rise of the catalyst temperature in an internal combustion engine.
FIG. 39 is a diagram illustrating a change in the ratio for removing exhaust gas components relative to the catalyst temperature TC, wherein the abscissa represents the catalyst temperature TC and the ordinate represents the removal ratio [%].
In FIG. 39, a solid line represents a ratio for removing CO (carbon monoxide) and HC (hydrocarbons) and a broken line represents a ratio for removing NOx (nitrogen oxides). When the catalyst temperature TC rises and reaches an activation starting temperature (=130xc2x0 C.), the removal ratio starts rising from 0%. When a completely activating temperature (=180xc2x0 C.) is reached, the removal ratio reaches nearly a maximum value (=98%).
In FIG. 38, the main body of the internal combustion engine 1 is provided with an intake pipe 2 for introducing the air into the engine and an exhaust pipe 3 for exhausting the exhaust gases burnt in the engine 1.
An air cleaner 4 is provided in an upstream portion of the intake pipe 2, and an air flow sensor 5 for detecting the amount Qa of the air taken in by the engine 1 is provided on the downstream side of the air cleaner 4.
A throttle valve 6 is provided in the intake pipe 2 on the downstream side of the air flow sensor 5 to adjust the amount Qa of the air that is taken in.
The intake pipe 2 is further provided with a by-path 7 by-passing the throttle valve 6, and an idling rotational speed control valve (hereinafter referred to as ISC valve) 8 for adjusting the opening degree of the by-path 7.
The ISC valve 8 adjusts the amount of the air taken in by-passing the throttle valve 6, so that the idling rotational speed of the engine 1 is controlled to assume a target value.
The exhaust pipe 3 is provided with an air-to-fuel ratio sensor 9 for detecting the oxygen concentration in the exhaust gases as an air-to-fuel ratio A/F.
On the downstream side of the exhaust pipe 3, furthermore, there are provided catalysts 10 and 11 for removing exhaust gas components relying upon the chemical reaction. The one catalyst 10 is provided in a hanging portion in the exhaust pipe 3 and another catalyst 11 is provided in the exhaust pipe 3 under the floor.
Generally, the catalysts 10 and 11 are called three-way catalysts, and work to oxidize CO and HC, and to reduce NOx, thereby to remove harmful components in the exhaust gases.
An intake portion corresponding to each cylinder of the engine 1 is provided with an injector 12 for injecting the fuel that is sent from a fuel pump (not shown).
The engine 1 is further provided with a crank angle sensor 13 that produces a crank angle signal CA corresponding to the rotational speed Ne of the engine.
Based on the operation condition data (amount Qa of the air taken in, air-to-fuel ratio A/F, crank angle signal CA, etc.) input from the sensors, an electronic control unit (hereinafter referred to as ECU) 14 including a microcomputer operates the control quantity for the engine 1, and produces a fuel injection signal J for driving the injector 12, an ISC control signal C for driving the ISC valve 8, an ignition signal P for driving an ignition device (described later) and the like signals.
Here, though not diagramed, a variety of sensors for detecting the operation conditions of the engine 1 include a water-temperature sensor for detecting the cooling water temperature TW of the engine, an intake-air-temperature sensor for detecting the temperature of the air taken in, and the like sensors.
The ignition device is constituted by spark plugs (not shown) provided in the cylinders of the engine 1, an ignition coil 15 connected to a battery to apply a high voltage to the spark plugs, and an igniter 16 which makes and breaks the spark coil 15 in response to the ignition signal P.
Next, described below is the operation of the conventional device for controlling the rise of the catalyst temperature in an internal combustion engine shown in FIG. 38.
First, the injector 12 injects the fuel of a required amount into the engine 1 depending upon the width of a drive pulse which is a fuel injection signal J. In response to the ignition signal P, furthermore, the igniter 16 makes and breaks the ignition coil 15 to apply a high voltage to the spark plug thereby to ignite the mixture in the cylinder.
At this moment, the amount of fuel injected from the injector 12 is calculated depending upon the amount Qa of the air taken in and the rotational speed Ne of the engine, and is corrected based on the air-to-fuel ratio A/F.
The ignition timing is set based on the amount Qa of the air taken in and the rotational speed Ne of the engine.
As is well known, furthermore, the fuel injection timing and the ignition timing are operated by using a pulse edge (reference crank angle position) of the crank angle signal CA as a timer control reference.
The mixture burnt in the engine 1 is exhausted as exhaust gases through the exhaust pipe 3, and from which harmful components are removed through the catalysts 10 and 11.
The temperature range in which the catalysts 10 and 11 are used is usually from about 130xc2x0 C. to about 900xc2x0 C.
When the temperatures of the catalysts 10 and 11 are to be quickly raised, in general, the ignition signal P is corrected by operation and the target ignition timing is corrected toward the delay side as disclosed in the above-mentioned known literature.
Upon delaying the ignition timing, the exhaust gases of a high temperature right after (or during) the combustion are exhausted into the exhaust pipe 3, and the temperatures of the catalysts 10 and 11 are quickly raised from the cold engine temperature up to an activating temperature.
During the idling operation condition, on the other hand, the throttle valve 6 is fully closed and the vehicle comes into a halt. The ECU 14, however, adjusts the opening degree of the ISC valve 8 to control the idling rotational speed.
That is, during the idling operation condition, the ECU 14 operates the amount of the air taken in through the by-path to obtain a target idling rotational speed and produces an ISC control signal C, and further corrects the ISC control signal C based on a deviation between a real engine rotational speed Ne and the target idling rotational speed in order to control the amount of the air taken in through the by-path (to control the opening degree of the ISC valve 8) by feedback.
When the engine 1 is cold, the target idling rotational speed is increased by a predetermined amount (100 rpm to 200 rpm) so that the engine 1 assumes a stable combustion.
In recent years, however, regulations against the exhaust gases have been reinforced as LEVs (low-emission vehicles) have been developed. To cope with the regulations, therefore, the catalyst temperatures must be raised up to the activating temperature more quickly. In quickly activating the catalysts, furthermore, it is required to avoid deterioration in the fuel efficiency and drivability.
According to the conventional device for controlling the rise of catalyst temperature in an internal combustion engine as described above, the temperature of the catalyst could not be very quickly raised despite the ignition timing was corrected toward the delay side and, hence, the exhaust gas components could not be removed to a degree that satisfies the exhaust gas regulations at the start or during the idling operation condition.
The present invention was accomplished in order to solve the above-mentioned problems, and its object is to provide a device for controlling the rise of the catalyst temperature in an internal combustion engine, which makes it possible to satisfy the exhaust gas regulations to a sufficient degree as a result of correcting the air-to-fuel ratio toward the lean side and increasing the idling rotational speed by an amount larger than that of when normally corrected toward the increasing side (normally controlled condition), so that the temperature of the catalyst can be quickly raised even at the start or during the idling operation condition.
The present invention provides a device for controlling the rise of the catalyst temperature in an internal combustion engine comprising:
a catalyst which is a three-way converter provided in an exhaust pipe of the internal combustion engine;
a catalyst temperature pick-up means for picking up data corresponding to the temperature of the catalyst as catalyst temperature;
a variety of sensors for detecting the operation conditions of said internal combustion engine;
an air-to-fuel ratio control means for controlling the air-to-fuel ratio of the internal combustion engine depending upon the operation conditions; and
an air-to-fuel ratio lean-correction means which, when said catalyst temperature is lower than a predetermined temperature corresponding to an activating temperature of said catalyst, corrects a target air-to-fuel ratio of said internal combustion engine toward the lean side to promote the activation of said catalyst;
wherein said variety of sensors detect at least intake-air-amount data corresponding to the load on said internal combustion engine and crank angle data corresponding to the rotational speed of said internal combustion engine; and
when the temperature of said catalyst is lower than said predetermined temperature, said air-to-fuel ratio lean-correction means sets said target air-to-fuel ratio to a lean activating air-to-fuel ratio which is larger than an air-to-fuel ratio of during the normally controlled operation and is higher than a stoichiometric air-to-fuel ratio.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said air-to-fuel ratio lean-correction means includes a first comparator means for comparing said catalyst temperature with a first predetermined temperature near said activating temperature, and a second comparator means for comparing said catalyst temperature with a second predetermined temperature which is higher than said first predetermined temperature and is corresponding to said activating temperature, and when said catalyst temperature lies within a range between said first predetermined temperature and said second predetermined temperature, said target air-to-fuel ratio is set to said lean activating air-to-fuel ratio.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said air-to-fuel ratio lean-correction means includes a tailing means for gradually changing said target air-to-fuel ratio when said target air-to-fuel ratio is to be changed over, and said tailing means gradually increases said target air-to-fuel ratio from an air-to-fuel ratio of during said normally controlled operation up to said lean activating air-to-fuel ratio every time by a predetermined value when said catalyst temperature is higher than said first predetermined temperature, and gradually decreases said target air-to-fuel ratio from said lean activating air-to-fuel ratio down to said air-to-fuel ratio of during said normally controlled operation every time by a predetermined value when said catalyst temperature is higher than said second predetermined temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said catalyst temperature pick-up means includes a temperature sensor that is provided on said catalyst to directly detect the temperature of said catalyst.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said catalyst temperature pick-up means includes an exhaust gas temperature sensor provided in the exhaust pipe of said internal combustion engine to detect the temperature of the exhaust gases, and a catalyst temperature estimating means for estimating the temperature of said catalyst based on said exhaust gas temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said catalyst temperature pick-up means includes a catalyst temperature estimating means for estimating the temperature of said catalyst based at least upon the intake-air-amount data of said internal combustion engine.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said catalyst temperature estimating means includes an initial temperature estimating means for estimating the initial temperature of said catalyst, and said initial temperature estimating means estimates the initial temperature of said catalyst based on at least the water temperature of said internal combustion engine at the start and the temperature of the air taken in at the start.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said initial temperature estimating means estimates the water temperature at the start as the initial temperature of said catalyst when the water temperature at the start is nearly equal to the temperature of the air taken in at the start, and estimates the initial temperature of said catalyst based on a deviation between the water temperature at the start and the temperature of the air taken in at the start when the water temperature at the start is different from the temperature of the air taken in at the start.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said catalyst temperature estimating means sets the water temperature of said internal combustion engine at the start as the initial catalyst temperature, and estimates said catalyst temperature based upon the amount of generated heat calculated from said intake-air-amount data and the heat capacity of the exhaust system inclusive of said exhaust pipe.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said predetermined temperature is set to a value which is obtained by adding a predetermined margin temperature to said catalyst activating temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said predetermined temperature is set to a value which is obtained by subtracting a predetermined margin temperature from said catalyst activating temperature.
The present invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine comprising:
a catalyst which is a three-way converter provided in an exhaust pipe of the internal combustion engine;
a catalyst temperature pick-up means for picking up data corresponding to the temperature of the catalyst as catalyst temperature;
a variety of sensors for detecting the operation conditions of said internal combustion engine;
an idling control means for controlling the idling rotational speed of said internal combustion engine depending upon said operation conditions; and
an idling rotational speed increasing means which, when said catalyst temperature is lower than a predetermined temperature corresponding to an activating temperature of said catalyst, corrects a target idling rotational speed of said internal combustion engine toward the increasing side higher than the idling rotational speed of during the normally controlled operation in order to promote the activation of said catalyst;
wherein, when said catalyst temperature is lower than said predetermined temperature, said idling rotational speed increasing means sets said target idling rotational speed to an increased activating rotational speed higher than the idling rotational speed of during said normally controlled operation for a predetermined period of time until said catalyst temperature reaches said activating temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said idling rotational speed increasing means includes a first comparator means for comparing said catalyst temperature with a first predetermined temperature lower than said activating temperature, and a second comparator means for comparing said catalyst temperature with a second predetermined temperature which is higher than said first predetermined temperature and is corresponding to said activating temperature, and sets said target idling rotational speed to said increased activating rotational speed when said catalyst temperature lies within a range between said first predetermined temperature and said second predetermined temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said idling rotational speed increasing means includes a tailing means for gradually changing said target idling rotational speed when said target idling rotational speed is to be changed over, and said tailing means gradually increases said target idling rotational speed from the idling rotational speed of during said normally controlled operation up to said increased activating rotational speed every time by a predetermined value when said catalyst temperature is higher than said first predetermined temperature, and gradually decreases said target idling rotational speed from said increased activating rotational speed down to the idling rotational speed of during said normally controlled operation when said catalyst temperature is higher than said second predetermined temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said catalyst temperature pick-up means includes a catalyst temperature estimating means for estimating the temperature of said catalyst based on at least the water temperature of said internal combustion engine at the start and the intake-air-amount data.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said idling rotational speed increasing means sets the increased activating rotational speed depending on the heat capacity of the exhaust system inclusive of said exhaust pipe.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said idling rotational speed increasing means sets, as said increased activating rotational speed, said target idling rotational speed to a value which is higher by about 100 rpm than the idling rotational speed of during the normally controlled operation.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, further comprising:
an air-to-fuel ratio control means for controlling the air-to-fuel ratio of said internal combustion engine depending upon the operation conditions; and
an air-to-fuel ratio lean-correction means for setting the target air-to-fuel ratio of said internal combustion engine to a lean activating air-to-fuel ratio which is larger than the air-to-fuel ratio of during the normally controlled operation and is larger than the stoichiometric air-to-fuel ratio when said catalyst temperature is lower than said predetermined temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, further comprising:
an ignition timing control means for controlling the ignition timing of said internal combustion engine depending upon the operation conditions; and
an ignition timing delaying means for correcting a target ignition timing of said internal combustion engine to a delayed activating ignition timing on the side delayed behind the ignition timing of during the normally controlled operation over a second predetermined period of time when said catalyst temperature is lower than said predetermined temperature.
The invention further provides a device for controlling the rise of the catalyst temperature in an internal combustion engine, wherein said ignition timing delaying means includes:
a first comparator means for comparing said catalyst temperature with a first predetermined temperature lower than said activating temperature;
a second comparator means for comparing said catalyst temperature with a second predetermined temperature higher than said first predetermined temperature and is corresponding to said activating temperature; and
a tailing means for gradually changing said target ignition timing when said target ignition timing is to be changed over;
wherein said tailing means gradually delays said target ignition timing from the ignition timing of during said normally controlled operation to said delayed activating ignition timing every time by a predetermined value when said catalyst temperature is higher than said first predetermined temperature, and gradually advances said target ignition timing from said delayed activating ignition timing to the ignition timing of during said normally controlled operation every time by a predetermined value when said catalyst temperature is higher than said second predetermined temperature.